Recently, printed electronics technology for manufacturing electronic devices by a method of forming various patterns by printing functional ink (hereinafter, collectively referred to as ink) on various types of substrates has attracted attention.
Such printed electronics technology has an advantage that the manufacturing process is not complicated, as compared with photolithography technology that has been used for forming patterns on a substrate. Further, a roll-to-roll printing apparatus that prints functional ink on a roll-shaped film or web (hereinafter, collectively referred to as a film) continuously supplied further increases production efficiency of electronic devices by a rapid production speed due to a continuous process.
In general, the roll-to-roll printing apparatus performs a coating process of applying ink so as to perform a printing process on a film. Such a coating process may be performed by a gravure method, a rotary screen method, a slot die method, or the like. Among them, the coating method using a slot die has advantages in that coating can be performed over a wide width all at once, there is no change in ink viscosity, no foreign matter is introduced, and the reproducibility of ink coating is excellent.
Meanwhile, printing accuracy is very important so as to manufacture an electronic device by using a printed electronics technology that prints ink on a substrate. In general, an electronic device requires a printing accuracy of several to several tens of microns (μm).
In general, a slot die coating apparatus, which performs a slot die coating process, requires ink to be thinly and uniformly applied to a substrate so as to improve the printing accuracy of an electronic device. To this end, it is important to quantitatively adjust ink supplied to a slot die according to a coating process condition and to coat a thin ink film to a desired thickness by adjusting a gap between the slot die and the substrate.
However, the conventional slot die coating apparatus adjusts a supply amount of ink in a state in which the coating process is temporarily stopped through the state of the substrate on which the coating process is performed, or adjusts a gap between the slot die and the substrate. Due to this, the conventional slot die coating apparatus cannot cope with various changes in the process condition during the coating process on the substrate, and thus, the coating uniformity of ink cannot be maintained.
In particular, in the case of a slot die coating apparatus used in a conventional roll-to-roll printing apparatus, when a film is deformed during a coating process due to external conditions such as heat or humidity and thus a register error occurs, a transfer speed and a tension of the film change for register control. Consequently, it has been difficult to thinly and uniformly apply ink to the substrate.
Therefore, there is a need for a slot die coating apparatus which is capable of monitoring a state of a slot die and a state of ink applied to a substrate in real time and is capable of thinly and uniformly applying ink to the substrate.